This article discusses the role of national supreme courts in the development of the European legal order, moving from a hierarchical to an interaction account of the relationship between legal systems. It first focuses on supreme courts' self-perception as European courts. For that purpose, it analyzes the loose understanding by national courts of the obligation to refer a question according to article 267 TFUE. This is done by looking not just at actual judicial practice, but more in general at the elaboration of a common understanding on the matter within transnational judicial networks. The article then contends that for national courts to assume responsibility in the development of the European legal order, extra-judicial interaction is necessary. It describes the contribution of judicial networks to the potential development of European judicial communities as a pre- condition for an integrated European legal order. It concludes by stressing the need for stronger empirical accounts in this field of research.